Simultaneous effects of night-time temperature and an allelochemical on performance of an insect herbivore

Abstract

One effect of global warming may be an increase in night-time temperatures with daytime temperatures remaining largely unchanged. We examined this potential effect of global warming on the performance of tobacco hornworm larvae, Manduca sexta (Sphingidae), by manipulating night-time temperature and dietary rutin levels simultaneously under a 12 light:12 dark photoregime. All four thermal regimes (26:14, 26:18, 26:22, and 26:26° C) had a daytime temperature of 26° C, with the night-time temperature increased from 14 to 26° C by increments of 4° C. Dietary rutin levels (0, 10 and 20 μmoles g fresh weight of diet) reflected those occurring naturally in the leaves of tomato, a preferred host plant of M. sexta. With low night-time temperatures (14 and 18° C), rutin had a negative linear effect on developmental rate, relative growth rate and relative consumption rate of the caterpillars. However, at a night-time temperature of 22° C, rutin had a negative non-linear effect. At a night-time temperature of 26° C, rutin had a negative linear impact but less so than at the other nightime temperatures. Likewise, the negative effect of rutin on molting duration was mitigated as night-time temperature increased. Final larval weight decreased linearly with increased dietary rutin concentrations. Total amount of food ingested was not affected by either rutin or thermal regime. As expected, the caterpillars developed faster under an alternating 26:14° C regime than a constant 20° C regime (the average temperature for the alternating regime), but the effect of rutin depended on the thermal regime. Switching daytime and night-time temperatures had no statistically significant effect on caterpillar performance. Overall, the effect of rutin on rates of larval performance was greater at some levels of warmer nights but damped at another level. These results indicate that the potential effect of warmer nights on insect performance is not a simple function of temperature because there can be interactions between night-time temperature and dietary allelochemicals.

Does Thermal Variability Experienced at the Egg Stage Influence Life History Traits across Life Cycle Stages in a Small Invertebrate?

“…This high survival may relate to recovery from heat injury during optimum nighttime temperatures [31] or inadequate damage to affect survival. Similar patterns of recovery under fluctuating temperatures have been found in other species [32], [33]. Wide fluctuations of temperature may improve survival under heat stress but delay egg development [34].…”

Response of Insect Herbivores to Multiple Allelochemicals Under Different Thermal Regimes

“…Although the negative effect of an allelochemical was often greater at the warm regime, it was most pronounced in some cases at the cool regime. We found that a very negative effect of high concentrations of rutin on developmental rate of M. sexta was greatly reduced with just a 4?C increase at night (Yang and Stamp 1995). 4B).…”

Effects of chlorogenic acid- and tomatine-fed caterpillars on performance of an insect predator

“…Only one other study addressed the simultaneous effects of temperature and diet on predatory insects, and that study used constant temperatures. The effects of food quality can be quite different at constant and alternating temperatures (Merkel 1977;Stamp 1994;Yang and Stamp 1995). For example, at an alternating thermal regime, increasing concentration of rutin reduced relative growth rate of Manduca sexta caterpillars whereas at a constant temperature (the average of the regime), rutin had no effect (Stamp 1994).…”